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Boeing 737
Airliner family by Boeing The Boeing 737 is a developed and manufactured by in the United States. Originally developed as a shorter, lower-cost twin-engine airliner derived from the and , the 737 has developed into a family of thirteen passenger models with capacities from 85 to 215 passengers. The 737 is Boeing's only narrow-body airliner in production, with the (-700, -800, and -900ER) and the re-engined and updated variants currently being built. The 737 was originally envisioned in 1964. The initial 737-100 made its first flight in April 1967, and entered airline service in February 1968 at . Next, the lengthened 737-200 entered service in April 1968. In the 1980s Boeing launched the longer 737-300, −400, and −500 variants (referred to as the series) featuring engines and wing improvements. The Boeing 737 Next Generation (NG) was introduced in the 1990s, with a redesigned, increased span wing, upgraded "glass" cockpit, and new interior. The 737 NG comprises the 737-600, −700, −800, and −900 variants, with lengths ranging from 31.09 to 42.06 m (102 to 138 ft). versions of the 737 NG are also produced. The 737 was revised again in the 2010s for greater efficiency, with the series featuring engines and improved . The 737 MAX entered service in 2017. The 737 series is the highest-selling commercial jetliner in history. The 737 has been continuously manufactured since 1967; the 10,000th was rolled out on March 13, 2018, a destined for , and over 4,600 orders are pending. Assembly of the 737 is performed at the in . Many 737s serve markets previously filled by , , , , and / airliners, and the aircraft currently competes primarily with the . As of 2006, there were an average of 1,250 Boeing 737s airborne at any given time, with two either departing or landing somewhere every five seconds. Contents ** ** ** ** ** ** ** ** *** 2.3.1 Winglets *** 2.4.1 Carbon brakes *** 2.4.2 Short-field design package ** *** 3.1.1 737-100 *** 3.1.2 737-200 ** ** ** ** ** ** ** ** *** 5.1.1 Units by generation * * * * ** ** * Development[] Background[] Boeing had been studying short-haul jet aircraft designs, and wanted to produce another aircraft to supplement the on short and thin routes. Preliminary design work began on May 11, 1964, and Boeing's intense market research yielded plans for a 50- to 60-passenger airliner for routes 50 to 1,000 mi (100 to 1,600 km) long. Initial design featured on the aft fuselage and a like the 727, and five-abreast seating, but engineer instead placed the engines under the wings to lighten the structure, enabling fuselage widening for six-abreast seating. The 737 design was presented in October 1964 at the maintenance and engineering conference by chief project engineer Jack Steiner, where its elaborate raised concerns about costs and dispatch reliability. The launch decision for the $150 million development was made by the board on February 1, 1965. became the launch customer on February 19, 1965, with an order for 21 aircraft, worth $67 million in 1965, after the airline received assurances from Boeing that the 737 project would not be canceled. Consultation with Lufthansa over the previous winter resulted in an increase in capacity to 100 seats. The prototype 737, a -100 operated by for testing On April 5, 1965, Boeing announced an order by for 40 737s. United wanted a slightly larger airplane than the original 737, so Boeing stretched the fuselage 36 in (91 cm) ahead of, and 40 in (102 cm) behind the wing. The longer version was designated 737-200, with the original short-body aircraft becoming the 737-100. Detailed design work continued on both variants at the same time. Boeing was far behind its competitors when the 737 was launched; rival aircraft , , and were already into flight certification. To expedite development, Boeing used 60% of the structure and systems of the existing 727, the most notable being the fuselage cross-section. This fuselage permitted six-abreast seating compared to the rival BAC-111 and DC-9's five-abreast layout. Design engineers decided to mount the directly to the underside of the wings to reduce the landing gear length and kept the engines low to the ground for easy ramp inspection and servicing. Many thickness variations for the engine attachment strut were tested in the wind tunnel and the most desirable shape for high speed was found to be one which was relatively thick, filling the narrow channels formed between the wing and the top of the nacelle, particularly on the outboard side. Originally, the span arrangement of the airfoil sections of the 737 wing was planned to be very similar to that of the 707 and 727, but somewhat thicker. A substantial improvement in drag at high Mach numbers was achieved by altering these sections near the nacelle. The engine chosen was the low-bypass ratio turbofan engine, delivering 14,500 (64 ) thrust. With the wing-mounted engines, Boeing decided to mount the on the fuselage rather than the style of the Boeing 727. Production and testing[] An early-production Boeing 737-100 of , the type's launch customer, at , 1968 The initial assembly of the Boeing 737 was adjacent to (now officially named King County International Airport) because the factory in was filled to capacity with the production of the 707 and 727. After 271 of the Boeing 737 aircraft were built, production was moved to Renton in late 1970. A significant portion of fuselage assembly—previously done by Boeing in Wichita, Kansas—is now performed by , which purchased some of Boeing's assets in Wichita. Key to increasing production efficiencies, the entire fuselage is shipped since the 737 Next Generation while it was sent in two pieces before. The fuselage is joined with the wings and landing gear and then moves down the assembly line for the engines, avionics, and interiors. After rolling out the aircraft, Boeing tests the systems and engines before a plane's to Boeing Field, where it is painted and fine-tuned before delivery to the customer. The first of six -100 prototypes rolled out in December 1966 and made its maiden flight on April 9, 1967, piloted by and Lew Wallick. On December 15, 1967, the certified the 737-100 for commercial flight, issuing Type Certificate A16WE. The 737 was the first aircraft to have, as part of its initial certification, approval for , which refers to an precision instrument approach and landing with a decision height between 98 to 197 feet (30 to 60 m). Lufthansa received its first aircraft on December 28, 1967. On February 10, 1968, Lufthansa became the first non-American airline to launch a new Boeing aircraft. was the only significant customer to purchase the 737-100. Only 30 aircraft were produced. The 737-200 had its maiden flight on August 8, 1967. It was certified by the FAA on December 21, 1967, and the inaugural flight for United was on April 28, 1968, from to . The lengthened -200 was widely preferred over the -100 by airlines. Sales were low in the early 1970s and, after a peak of 114 deliveries in 1969, only 22 737s were shipped in 1972 with 19 in backlog. The saved the program by ordering . African airline orders kept the production running until the 1978 US where demand was better for a six-abreast narrow-body aircraft, particularly re-engined with the , struggling at the time. Initial derivatives[] An early-production, retrofitted 737-200 with deployed thrust reversers The original engine nacelles incorporated thrust reversers taken from the 727 outboard nacelles. They proved to be relatively ineffective and tended to lift the aircraft up off the runway when deployed. This reduced the downforce on the main wheels thereby reducing the effectiveness of the wheel brakes. In 1968, an improvement to the system was introduced. A 48-inch tailpipe extension was added and new, target-style, thrust reversers were incorporated. The thrust reverser doors were set 35 degrees away from the vertical to allow the exhaust to be deflected inboard and over the wings and outboard and under the wings. The improvement became standard on all aircraft after March 1969, and a retrofit was provided for active aircraft. Boeing fixed the drag issue by introducing new longer nacelle/wing fairings, and improved the airflow over the flaps and slats. The production line also introduced an improvement to the flap system, allowing increased use during takeoff and landing. All these changes gave the aircraft a boost to payload and range, and improved short-field performance. In May 1971, after aircraft #135, all improvements, including more powerful engines and a greater fuel capacity, were incorporated into the 737-200, giving it a 15% increase in payload and range over the original -200s. This became known as the 737-200 Advanced, which became the production standard in June 1971. 737-200 planform In 1970, Boeing received only 37 orders. Facing financial difficulties, Boeing considered closing the 737 production-line and selling the design to Japanese aviation companies. After the cancellation of the , and scaling back of 747 production, enough funds were freed up to continue the project. In a bid to increase sales by offering a variety of options, Boeing offered a 737C (Convertible) model in both -100 and -200 lengths. This model featured a 134 in × 87 in (340 cm × 221 cm) freight door just behind the cockpit, and a strengthened floor with rollers, which allowed for . A 737QC (Quick Change) version with palletized seating allowed for faster configuration changes between cargo and passenger flights. With the improved short-field capabilities of the 737, Boeing offered the option on the -200 of the , which enables this aircraft to operate on remote, unpaved runways. Until retiring its -200 fleet in 2007, used this option for some of its rural operations in . Northern Canadian operators , , , and still operate the gravel kit aircraft in Northern Canada, where gravel runways are common. In 1988, the initial production run of the -200 model ended after producing 1,114 aircraft. The last one was delivered to on August 8, 1988. Improved variants[] Main article: Development began in 1979 for the 737's first major revision. Boeing wanted to increase capacity and range, incorporating improvements to upgrade the aircraft to modern specifications, while also retaining commonality with previous 737 variants. In 1980, preliminary aircraft specifications of the variant, dubbed 737-300, were released at the . The 737-300 was the first Classic variant Boeing engineer Mark Gregoire led a design team, which cooperated with to select, modify and deploy a new engine and nacelle that would make the 737-300 into a viable aircraft. They chose the engine to power the aircraft, which yielded significant gains in fuel economy and a reduction in noise, but also posed an engineering challenge, given the low ground clearance of the 737 and the larger diameter of the engine over the original Pratt & Whitney engines. Gregoire's team and CFM solved the problem by reducing the size of the fan (which made the engine slightly less efficient than it had been forecast to be), placing the engine ahead of the wing, and by moving engine accessories to the sides of the engine pod, giving the engine a distinctive non-circular "" air intake. Earlier customers for the CFM56 included the U.S. Air Force with its program to re-engine KC-135 tankers. The passenger capacity of the aircraft was increased to 149 by extending the fuselage around the wing by 9 feet 5 inches (2.87 m). The wing incorporated several changes for improved aerodynamics. The wingtip was extended 9 in (23 cm), and the wingspan by 1 ft 9 in (53 cm). The leading-edge slats and trailing-edge flaps were adjusted. The tailfin was redesigned, the flight deck was improved with the optional EFIS (Electronic Flight Instrumentation System), and the passenger cabin incorporated improvements similar to those developed on the . The prototype −300, the 1,001st 737 built, first flew on February 24, 1984 with pilot Jim McRoberts. It and two production aircraft flew a nine-month-long certification program. In June 1986, Boeing announced the development of the 737-400, which stretched the fuselage a further 10 ft (3.0 m), increasing the passenger load to 188. The -400s first flight was on February 19, 1988, and, after a seven-month/500-hour flight-testing run, entered service with that October. 737-400 at takeoff. The stubbier engines are mounted ahead of the wings. The -500 series was offered, due to customer demand, as a modern and direct replacement of the 737-200. It incorporated the improvements of the 737 Classic series, allowing longer routes with fewer passengers to be more economical than with the 737-300. The fuselage length of the -500 is 1 ft 7 in (48 cm) longer than the 737-200, accommodating up to 140 passengers. Both glass and older-style mechanical cockpits arrangements were available. Using the CFM56-3 engine also gave a 25% increase in over the older -200s P&W engines. The 737-500 was launched in 1987 by , with an order for 20 aircraft, and flew for the first time on June 30, 1989. A single prototype flew 375 hours for the certification process, and on February 28, 1990, received the first delivery. After the introduction of the −600/700/800/900 series, the −300/400/500 series was called the 737 Classic series. The price of jet fuel reached a peak in 2008, when airlines devoted 40% of the retail price of an air ticket to pay for fuel, versus 15% in 2000. Consequently, in that year carriers retired Classic 737 series aircraft to reduce fuel consumption; replacements consisted of more efficient Next Generation 737s or /A319/A318 series aircraft. On June 4, 2008, announced it would retire all 94 of its Classic 737 aircraft (64 737-300 and 30 737-500 aircraft), replacing them with jets taken from its subsidiary, which has been shut down. Next-Generation models[] Main article: Prompted by the new , Boeing initiated development of an updated series of aircraft in 1991. After working with potential customers, the 737 Next Generation (NG) program was announced on November 17, 1993. The 737NG encompasses the -600, -700, -800, and -900, and is to date the most significant upgrade of the airframe. The performance of the 737NG is, in essence, that of a new aircraft, but important commonality is retained from previous 737 models. Boeing 737NG fuselage being transported by rail The wing was redesigned with a new section, greater , increased wing span by 16 ft (4.9 m) and area by 25%, which increased total fuel capacity by 30%. New, quieter, more fuel-efficient engines were used. The wing, engine, and fuel capacity improvements combined increase the 737's range by 900 nautical miles (1,700 km) to over 3,000 nautical miles (5,600 km), now permitting transcontinental service. With the increased fuel capacity, higher (MTOW) specifications are offered. The 737NG included redesigned vertical stabilizers, and were available on most models. The flight deck was upgraded with modern avionics, and passenger cabin improvements similar to those on the , including more curved surfaces and larger overhead bins than previous-generation 737s. The Next Generation 737 interior was also adopted on the . The first NG to roll out was a -700, on December 8, 1996. This aircraft, the 2,843rd 737 built, first flew on February 9, 1997. The prototype -800 rolled out on June 30, 1997, and first flew on July 31, 1997. The smallest of the new variants, the -600s, is the same size as the -500. It was the last in this series to launch, in December 1997. First flying January 22, 1998, it was given certification on August 18, 1998. A flight test program was operated by 10 aircraft; 3 -600s, 4 -700s, and 3 -800s. Boeing 737-700 in –Boeing livery, showing blended winglets available on the 737 Next Generation models In 2004, Boeing offered a Short Field Performance package in response to the needs of , which frequently operates from restricted airports. The enhancements improve takeoff and landing performance. The optional package is available for the 737NG models and standard equipment for the 737-900ER. The CFM56-7B Evolution nacelle began testing in August 2009 to be used on the new 737 PIP (Performance Improvement Package) due to enter service mid-2011. This new improvement is said to shave at least 1% off overall drag and have some weight benefits. Overall, it is claimed to have a 2% improvement on fuel burn on longer stages. In 2010, new interior options for the 737NG included the -style Boeing Sky Interior. Boeing delivered the 5,000th 737 to on February 13, 2006, the 6,000th 737 to in April 2009, the 8,000th 737 to on April 16, 2014. The Airbus A320 family has outsold the 737NG over the past decade, although its order totals include the A321 and A318, which have also rivaled Boeing's and , respectively. The 737NG has also outsold the A320 on an annual basis in past years, with the next generation series extending the jetliner's run as the most widely sold and commonly flown airliner family since its introduction. The 10,000th aircraft was ordered in July 2012. Boeing produces 42 of the type per month in 2015, and expects to increase to 52 per month in 2018. The slow selling 737-600 is no longer being marketed and was removed from the Boeing website as of 2016update, its position as the smallest model being taken by the more popular 737-700. The 737, particularly the , has been featured in many flight simulation games, including and . Replacement or re-engining[] Main articles: and Since 2006, Boeing has discussed replacing the 737 with a "clean sheet" design (internally named "Boeing Y1") that could follow the . A decision on this replacement was postponed, and delayed into 2011. In November 2014, it was reported that Boeing plans to develop a new aircraft to replace the 737 in the 2030 time frame. The airplane is to have a similar fuselage, but probably made from composite materials similar to the . Boeing also considers a parallel development along with the 757 replacement, similar to the development of the 757 and 767 in the 1970s. On July 20, 2011, Boeing announced plans for a new 737 version to be powered by the engine, with intending to order 100 of these aircraft. On August 30, 2011, Boeing confirmed the launch of the 737 new engine variant, called the , with new CFM International LEAP-1B engines. On September 23, 2015, Boeing announced a collaboration with to build a completion and delivery facility for the 737 in China, the first outside the U.S. This facility initially handles interior finishing only, but will subsequently be expanded to include paintwork. The first 737 MAX was delivered from the facility to Air China on December 15, 2018. Design[] Boeing 737-700 showing the retracted and engine with flattened underside and triangular shape The 737's main landing gear under the wings at mid-cabin rotates into wells in the aircraft's belly. The legs are covered by partial doors, and "brush-like" seals aerodynamically smooth (or "fair") the wheels in the wells. The sides of the tires are exposed to the air in flight. "Hub caps" complete the aerodynamic profile of the wheels. It is forbidden to operate without the caps, because they are linked to the ground speed sensor that interfaces with the anti-skid brake system. The dark circles of the tires are clearly visible when a 737 takes off, or is at low altitude. As the 737's fuselage design is derived from that of the , it inherited the distinctive 'eyebrow windows' used on the larger airliner, situated just above the windscreen. 737s are not equipped with . The original aircraft were too small to require them, and adding a fuel dump system to the later, larger variants would have incurred a large weight penalty. Boeing instead demonstrated an "equivalent level of safety". Depending upon the nature of the emergency, 737s either circle to burn off fuel or land overweight. If the latter is the case, the aircraft is inspected by maintenance personnel for damage and then returned to service if none is found. Engines[] Engines on the 737 Classic series (−300, −400, −500) and Next-Generation series (−600, −700, −800, −900) do not have circular inlets like most aircraft. The 737 Classic series featured engines, which yielded significant gains in fuel economy and a reduction in noise over the engines used on the −100 and −200, but also posed an engineering challenge given the low ground clearance of the 737. Boeing and engine supplier solved the problem by placing the engine ahead of (rather than below) the wing, and by moving engine accessories to the sides (rather than the bottom) of the engine pod, giving the 737 a distinctive non-circular air intake. The wing also incorporated changes for improved aerodynamics. The engines' accessory was moved from the 6 o'clock position under the engine to the 4 o'clock position (from a front/forward looking aft perspective). This side-mounted gearbox gives the engine a somewhat triangular rounded shape. Because the engine is close to the ground, 737-300s and later models are more prone to engine (FOD). The improved turbofan engine on the 737 Next Generation is 7% more fuel-efficient than the previous CFM56-3 in the 737 classics. The newest 737 variants, the 737 MAX family, are to feature engines with a 68 inches (1.73 m) fan diameter. These engines are expected to be 10-12% more efficient than the CFM56-7B engines on the 737 Next Generation family. 737-200 JT8D engine with original cowling design 737-800 CFM56 engine with ovoid "hamster pouch" inlet 737 MAX 9 CFM LEAP-1B engine with 787-derived engine chevrons Flight systems[] The are intrinsically safe. In the event of total hydraulic system failure or double engine failure, they will automatically and seamlessly revert to control via . In this mode, the servo tabs aerodynamically control the elevators and ailerons; these servo tabs are in turn controlled by cables running to the control yoke. The pilot's muscle forces alone control the tabs. For the 737 Next Generation, a six-screen LCD with modern avionics was implemented while retaining crew commonality with previous generation 737. Most 737 cockpits were delivered with "eyebrow windows" positioned above the main glareshield, which were a feature of the original 707 and 727 to allow for better crew visibility. Contrary to popular belief, these windows were not intended for (only the military T-43A had a sextant port for star navigation, which the civilian models lacked). With modern avionics, the windows became redundant, and many pilots actually placed newspapers or other objects in them to block out sun glare. They were eliminated from the 737 cockpit design in 2004, although they are still installed on customer request. The eybrow windows are sometimes removed and plugged, usually during maintenance overhauls, and can be distinguished by the metal plug which differs from the smooth metal in later aircraft that were not originally fitted with the windows. Original 737-200 cockpit Classic 737-300 cockpit Next Generation 737-800 cockpit Upgrade packages[] Winglets[] The 737 has four different winglet types: 737-200 Mini-winglet, 737 Classic/NG Blended Winglet, 737 Split Scimitar Winglet, and 737 MAX Advanced Technology Winglet. The 737-200 Mini-winglets are part of the Quiet Wing Corp modification kit that received certification in 2005. Blended are in production on 737 NG aircraft and are available for retrofit on 737 Classic models. These winglets stand approximately 8 feet (2.4 m) tall and are installed at the wing tips. They help to reduce fuel burn (by reducing drag), engine wear, and takeoff noise. Overall fuel efficiency improvement is up to five percent through the reduction of lift-induced drag. Split Scimitar winglets became available in 2014 for the 737-800, 737-900ER, BBJ2 and BBJ3, and in 2015 for the 737-700, 737-900 and BBJ1. Split Scimitar winglets were developed by (API), the same Seattle based corporation that developed the blended winglets; the Split Scimitar winglets produce up to a 5.5% fuel savings per aircraft compared to 3.3% savings for the blended winglets. Southwest Airlines flew their first flight of a 737-800 with Split Scimitar winglets on April 14, 2014. The next generation 737, 737 MAX, will feature an Advanced Technology (AT) Winglet that is produced by Boeing. The Boeing AT Winglet resembles a cross between the Blended Winglet and the Split Scimitar Winglet. 737 Blended Winglet on an Next Generation 737 737 Split Scimitar Winglet on an Next Generation 737 737 MAX Advanced Technology Winglet Flight systems[] Carbon brakes[] As of July 2008update the 737 features carbon manufactured by . These new brakes, now certified by the , weigh 550–700 lb (250–320 kg) less than the steel brakes normally fitted to the Next-Gen 737s (weight savings depend on whether standard or high-capacity brakes are fitted). A weight reduction of 700 pounds on a Boeing 737-800 results in 0.5% reduction in fuel burn. Short-field design package[] A short-field design package is available for the 737-600, -700, and -800, allowing operators to fly increased payload to and from airports with runways under 5,000 feet (1,500 m). The package consists of sealed (improved lift), a two-position tail skid (enabling greater protection against tail strikes that may be caused by the lower landing speeds), and increased flight spoiler deflection on the ground. These improvements are standard on the 737-900ER. Interior[] The 737 interior arrangement has changed in successive generations. The original 737 interior was restyled for the 737 Classic models using 757 designs, while 777 architecture was used for the debut of the Next Generation 737. Designed using Boeing's new cabin concepts, the latest Sky Interior features sculpted sidewalls and redesigned window housings, along with increased headroom and LED . Larger pivot-bins similar to those on the 777 and 787 have more luggage space than prior designs. The Sky Interior is also designed to improve cabin noise levels by 2–4 . The first 737 equipped with the Boeing Sky Interior was delivered to in late 2010. Continental Airlines,, , and have also received Sky Interior-equipped 737s. 737 Classic interior in 3–3 economy class layout Boeing 737NG standard interior with curved panels Boeing 737NG Sky Interior with pivot bins and LED lighting Variants[] The 737 models can be divided into four generations, including thirteen major variants. The "Original" models consist of the 737-100, 737-200/-200 Advanced. The "Classic" models consist of the 737-300, 737-400, and 737-500. The "Next Generation" variants consist of the 737-600, 737-700/-700ER, 737-800, and 737-900/-900ER. Of these variants, many feature additional versions such as the T-43, which was a modified Boeing 737-200 used by the United States Air Force (USAF). The fourth generation derivative - the 737 MAX - consists of the 737-MAX-7, 737-MAX-8, and 737-MAX-9 which will replace the -700, -800 and -900/900ER versions of the NG family, respectively. A fourth MAX variant, the 737-MAX-10 is currently under development and is the largest 737 to date. 737 Original series[] 737-100 737-100[] The initial model was the 737-100. It was launched in February 1965. The -100 was rolled out on January 17, 1967, had its first flight on April 9, 1967 and entered service with in February 1968. The aircraft is the smallest variant of the 737. A total of 30 737-100s were ordered and delivered; the final commercial delivery took place on October 31, 1969 to . No 737-100s remain in commercial service. The original Boeing prototype, last operated by and retired more than 30 years after its maiden flight, is on exhibit in the in Seattle. 737-200[] The 737-200 is a 737-100 with an extended fuselage, launched by an order from in 1965. The -200 was rolled out on June 29, 1967, and entered service with United in April 1968. The 737-200 Advanced is an improved version of the -200, introduced into service by on May 20, 1971. The -200 Advanced has improved aerodynamics, automatic wheel brakes, more powerful engines, more fuel capacity, and longer range than the -100. Boeing also provided the 737-200C (Cargo), which allowed for conversion between passenger and cargo use and the 737-200QC (Quick Change), which facilitated a rapid conversion between roles. The 1,095th and last delivery of a -200 series aircraft was in August 1988 to . Many 737-200s have been phased out or replaced by newer 737 versions. In July 2018, there were a combined 58 Boeing 737-200s in service, mostly with "second and third tier" airlines, and those of developing nations. 737-200 Advanced With a modification the 737-200 can use unimproved or unpaved landing strips, such as gravel runways, that other similarly-sized jet aircraft cannot. Gravel-kitted 737-200 Combis are currently used by , , , and in northern Canada. For many years, made use of gravel-kitted 737-200s to serve Alaska's many unimproved runways across the state. Nineteen 737-200s, designated , were used to train aircraft navigators for the . Some were modified into CT-43s, which are used to transport passengers, and one was modified as the NT-43A Radar Test Bed. The first was delivered on July 31, 1973 and the last on July 19, 1974. The ordered three modified 737-200s, designated Boeing 737-2x9 Surveiller. They were used as Maritime reconnaissance (MPA)/transport aircraft, fitted with SLAMMAR (Side-looking Multi-mission Airborne Radar). The aircraft were delivered between May 1982 and October 1983. After 40 years the final 737-200 aircraft in the U.S. flying scheduled passenger service were phased out in March 2008, with the last flights of . The variant still sees regular service through North American charter operators such as . 737 Classic series[] Main article: 737-300, the midsize 737 Classic The Boeing 737 Classic is the name given to the -300/-400/-500 series of the Boeing 737 after the introduction of the -600/700/800/900 series. The Classic series was originally introduced as the 'new generation' of the 737. Produced from 1984 to 2000, 1,988 aircraft were delivered. 737 Next Generation[] Boeing Main article: By the early 1990s, it became clear that the new was a serious threat to Boeing's market share, as Airbus won previously loyal 737 customers such as Lufthansa and United Airlines. In November 1993, Boeing's board of directors authorized the Next Generation program to replace the 737 Classic series. The -600, -700, -800, and -900 series were planned. After engineering trade studies and discussions with major 737 customers, Boeing proceeded to launch the 737 Next Generation series in late 1993, with 6,856 built as of September 2017update. Variants include the . 737 MAX[] Boeing 8 Main article: The is the fourth generation of the 737, succeeding the (NG). After launched the in December 2010, achieving 1,029 orders by June 2011 and breaking Boeing's monopoly with with an order for 130 A320neos that July, Boeing launched the program on August 30, 2011. The first flight was on January 29, 2016. It gained FAA certification on March 8, 2017. The first delivery was a MAX -8 on May 6, 2017 to , which put it into service on May 22, 2017. The 737 MAX is based on earlier 737 designs. The MAX is with more efficient -1B powerplants, aerodynamic improvements (most notably split-tip ), and airframe modifications. The 737 MAX series is offered in four lengths, typically offering 138 to 230 seats and a 3,215 to 3,825 nmi (5,954 to 7,084 km) range. The 737 MAX 7, MAX 8, and MAX 9 replace, respectively, the 737-700, -800, and -900. Additional length is offered with the further stretched 737 MAX 10. As of September 2018update, the Boeing 737 MAX has received 4,783 firm orders. Boeing Business Jet (BBJ)[] BBJ cabin Main article: The Boeing Business Jet is a customized version of the 737. Plans for a business jet version of the 737 are not new. In the late 1980s, Boeing marketed the 77-33 jet, a business jet version of the 737-300. The name was short-lived. After the introduction of the next generation series, Boeing introduced the Boeing Business Jet (BBJ) series. The BBJ1 was similar in dimensions to the 737-700 but had additional features, including stronger wings and landing gear from the 737-800, and had increased range (through the use of extra fuel tanks) over the other 737 models. The first BBJ rolled out on August 11, 1998 and flew for the first time on September 4. On October 11, 1999 Boeing launched the BBJ2. Based on the 737-800, it is 19 feet 2 inches (5.84 m) longer than the BBJ, with 25% more cabin space and twice the baggage space, but has slightly reduced range. It is also fitted with auxiliary belly fuel tanks and winglets. The first BBJ2 was delivered on February 28, 2001. Boeing's BBJ3 is based on the 737-900ER. The BBJ3 has 1,120 square feet (104 m) of floor space, 35% more interior space, and 89% more luggage space than the BBJ2. It has an auxiliary fuel system, giving it a range of up to 4,725 nautical miles (8,751 km), and a . Boeing completed the first example in August 2008. This aircraft's cabin is pressurized to a simulated 6,500-foot (2,000 m) altitude. Freighter[] Boeing is studying plans to offer passenger to freighter conversion for the 737-800. Boeing has signed an agreement with Chinese YTO Airlines to provide the airline with 737-800 Boeing Converted Freighters (BCFs) pending a planned program launch. In 2016, Boeing officially launched the 737-800BCF program, converting old passenger jets to dedicated freighters. The first aircraft was delivered in 2018 to GECAS, which is leased to . Operators[] Qantas Boeing 737-400 landing at In March 2018, the 10,000th 737 was rolled out as over 4,600 orders are pending. The 737 is operated by more than 500 airlines, flying to 1,200 destinations in 190 countries: over 4,500 are in service and at any given time there are on average 1,250 airborne worldwide. On average, somewhere in the world, a 737 took off or landed every five seconds in 2006. Since entering service in 1968, the 737 has carried over 12 billion passengers over 74 billion miles (120 billion km; 65 billion nm), and has accumulated more than 296 million hours in the air. The 737 represents more than 25% of the worldwide fleet of large commercial jet airliners. Civilian[] Main article: As of July 2018update, 58 Boeing 737-200 aircraft were in civilian service. Military[] A United States Navy C-40A, a variant of the 737-700C A PLAAF 737 electronic signals intelligence (ELINT) version Many countries operate the 737 passenger, BBJ, and cargo variants in government or military applications. Users with 737s include: * * * * * * * * * * * * * * * * * * * * * * * Competition[] The Boeing 737 Classics and the Boeing 737 Next Generation have faced main challenges from the introduced in 1988, which was developed to compete also with the McDonnell Douglas MD-80/90 series and the (formerly named McDonnell Douglas MD-95). Boeing has delivered over 10,077 aircraft of the 737 family since late 1967, with over 8,210 of those deliveries since March 1, 1988, and has a further 4,648 on firm order as of May 2018update. In comparison, has delivered 7,771 A320 series aircraft since their certification/first delivery in early 1988, with another 5,520 on firm order (as of September 2017update). Further information: Orders and deliveries[] Total production[] In total, 10,444 units of the Boeing 737 have been delivered as of December 31, 2018update. Units by generation[] As of December 2018update, 15,207 units of the Boeing 737 have been ordered, with 4,763 units are to be delivered. Units built by model type for 737 Original, Classic, Next Generation, and Boeing Business Jet families are as follows: